Generally, in a planographic printing plate called as a negative type, a planographic printing plate is prepared by curing the image portion after image exposure, followed by being subjected to a washing treatment with water and a finisher gum treatment after the unexposed portion having been removed by dissolution. In recent years, to obtain a high resolution and a high sharpness, studied has been a method in which a planographic printing plate is prepared by digital exposure employing a laser light based on image information followed by a development process. For example, it is a system in which a planographic printing plate is prepared by modulating an exposure light source according to image signals transmitted through a communication circuit or output signals from such as an electrophotographic plate making system and an image processing system and by performing exposure on a photosensitive material by means of direct scanning exposure.
However, there was a problem that spectral sensitization and sensitivity increase to match a wavelength of a laser light for digital exposure were difficult.
In recent years, as materials which are suitable to laser exposure and capable of being spectrally sensitized and sensitivity increased, a planographic printing plate material provided with a photopolymerizable photosensitive layer containing a photopolymerization initiator has come to be noted. Further sensitivity increase is required to shorten the recording time with respect to such plate materials for CTP (Computer to Plate) which record digital data with a laser light source. Heretofore, plate materials having high printing durability are desired in many printing applications as newspaper printing and commercial printing of such as advertisement.
There are proposed techniques (refer to, for example, patent literatures 1 and 2) in which a titanocene compound is utilized as a photopolymerization initiator to achieve sensitivity increase. However, sufficient sensitivity increase has not been achieved by only these techniques.
Further, for the purpose of sensitivity improvement, there have been proposed a technique (refer to, for example, patent literature 3) in which a monomer provided with a tertiary amino group in the structure (a monomer containing an addition polymerizable ethylenic double bond) and a trihalogenated methyl-s-triazine compound are utilized in combination, and a technique (refer to, for example, patent literature 4) in which a metalocene compound such as titanocene in addition to a monomer provided with a tertiary amino group in the structure (a monomer containing an addition polymerizable ethylenic double bond) and a trihalogenated methyl-s-triazine compound are utilized in combination.
Among these metalocene compounds, titanocene has a relatively high sensitivity and excellent printing durability, while a Fe arene complex compound has a problem of poor printing durability and has not been studied so much although it is cheaper compared to titanocene.
Further, it is necessary to improve adhesion between a photosensitive layer and a support to increase printing durability, and preferable is to coat a photosensitive layer after anodic oxidation for the purpose of improving adhesion, however, excessively strong adhesion caused a problem that the photosensitive layer of an unexposed portion cannot be peeled off or dissolved completely to generate ink smudge. Many patents have been applied with respect to roughening and anodic oxidation of an aluminum support (refer to, for example, patent literatures 5 and 6).
However, a detailed study has not been performed yet with respect to the relationship between the type a Fe allene complex compound, which is employed as a photopolymerization initiator, and a roughening treatment of an aluminum support.
[Patent Literature 1]JP-A No. 2001-209170(Hereinafter, JP-A refers to Japanese Patent Publication Opento Public Inspection)[Patent Literature 2]JP-A No. 2001-183822[Patent Literature 3]JP-A No. 1-105238[Patent Literature 4]JP-A No. 2-127404[Patent Literature 5]JP-A No. 10-37000[Patent Literature 6]JP-A No. 9-142049